Plasticity and Reorganization of the Brain Post Stroke Robert Teasell, Nestor A. Bayona, and Jamie Bitensky Top Stroke Rehabil 2005;12(3):11–26 © 2005 Thomas Land Publishers, Inc. www.thomasland.com Reorganization of the cortex post stroke is dependent not only on the lesion site but also on remote brain areas that have structural connections with the area damaged by the stroke. Motor recovery is largely dependent on the intact cortex adjacent to the infarct, which points out the importance of preserving the penumbral areas. There appears to be a priority setting with contralateral and ipsilateral motor pathways, with ipsilateral (unaffected hemisphere) pathways only becoming prominent after more severe strokes where functional contralateral (affected hemisphere) pathways are unable to recover. Ipsilateral or unaffected hemisphere motor pathway activation is therefore associated with a worse prognosis. Key words: animal models, cerebral vascular accident, humans, neuronal plasticity, recovery of function 11 Robert Teasell, MD, FRCPC, is Professor and Chair-Chief, Department of Physical Medicine and Rehabilitation, St. Joseph’s Health Care and the University of Western Ontario, London, Ontario, Canada. Nestor A. Bayona, MSc (Neuroscience), is Research Associate, Department of Physical Medicine and Rehabilitation, St. Joseph’s Health Care and the University of Western Ontario, London, Ontario, Canada. Jamie Bitensky, MSc (OT), is Research Associate, Department of Physical Medicine and Rehabilitation, St. Joseph’s Health Care and the University of Western Ontario, London, Ontario, Canada, and Royal Victoria Hospital, Montreal, Quebec, Canada. A s we have seen in the previous article, the uninjured brain has mechanisms for reorganization and plasticity associated with retraining or experience; these mechanisms also compensate for neuronal loss due to aging. A stroke presents the brain with a much more difficult challenge. A cerebral infarct results in the sudden loss of a significant number of neurons and synaptic connections. 1 The magnitude of this loss in such a focal area is problematic. Reorganization of the remaining injured brain is very important for recovery to occur. As the population ages, there will be an increasing number of individuals with stroke-related impair- ments and disabilities who will benefit from reha- bilitation. Recovery in these cases can be defined as either neurological recovery or functional recovery. Neurological recovery is a direct result of brain repair or reorganization that generally occurs for the first weeks to months post stroke but can continue for several months after the event. This article will attempt to compare the animal and clinical research in post stroke recovery and will focus on the evi- dence that exists for neurological recovery, in par- ticular cortical reorganization post stroke. Defining Recovery and Time Course Post Stroke Brosseau et al. 2 have noted that an understand- ing of the patterns of neuropsychological and physical recovery time post stroke will allow reha- bilitation specialists to provide more effective therapy and improve use of resources during the patient’s stay in hospital. Partridge et al. 3 have also suggested that an understanding of recovery and potential influencing factors can assist in the set- ting of effective therapeutic strategies. Defining Different Types of Recovery Spontaneous or intrinsic neurological recovery Neurological recovery is a complex process and is discussed in detail later in this article. The Copenhagen Stroke Study showed that the rate of neurological recovery is directly related to the ini- tial stroke severity. 4–6 Table 1 summarizes the re- sults from the Copenhagen Stroke Study and de-